OBJECTIVE: To understand the neural system underlying the expression of emotion in primates. RESULTS We have focused on elucidating mechanisms underlying the expression of fear and anxiety. This is an area of great importance because, when appropriate, fear-motivated behaviors are adaptive; however, when overly intense or expressed out of context, extreme fear is characteristic of many forms of psychopathology. We are using state-of-the-art techniques to understand the role of the amygdala and its nuclei in mediating fearful states. We will assess the role of the amygdala in mediating 1) classically conditioned autonomic responses, 2) ethologically relevant threatening stimuli, and 3) affiliative and defensive behavior expressed in social situations. This year fifteen monkeys have been lesioned using ibotenic acid. These axon sparing lesions are resulting in more subtle alterations then those reported with more destructive lesioning. Specifically, the data suggests that amygdala lesions disrupt the ability to express learned fears. Eventually, these studies will define biological mechanisms regulating the expression of the primate's adaptive responding to threatening stimuli. These findings will provide insight into mechanisms mediating maladaptive responding in humans, which is characteristic of fear-related psychopathology. FUTURE DIRECTIONS Histological analysis of all lesions will be performed to correlate site and extent of lesions with effects. Other studies will examine the effects of reversible inactivation of the amygdala with lidocaine. KEY WORDS neurobiology, amygdala, defense, behavior, brain, psychopathology, conditioning